The proposed research is planned within two main categories. The first will analyse the effects of hippocampal damage in adult monkeys while the second will be concerned with the effects of equivalent lesions as a function of age. Experiments in the first category will attempt to: 1. Find out whether the physiological mechanisms subserving memory are organized as a mosaic of modality and task specific processes or whether the impairments which follow brain damage in monkeys reflect interference with a unitary system localised in the hippocampus which is involved in each of the specific impairments. To this end, the effects of hippocampal, frontal and inferotemporal lesions will be compared on a series of spatial and non-spatial retention tests in the visual and tactual modalities. 2. Continue the study of spatial impairment which follows hippocampal damage by analyzing anatomical pathways beyond the hippocampus. These experiments will assess the effects of selective lesions of the septum and the mammillary bodies on spatial reversal learning. 3. Identify possible motivational post- operative changes such as stimulus satiation. In the second category, it is intended to determine whether early hippocampal damage will affect differentially performance on spatial and non-spatial tasks and to study the development of spatial orientation, reversal learning and retention of discrimination tasks in normal infants.